TABLE 3

The enzyme kinetic parameters for seven UGT1A isoforms showing substrate inhibition

The initial rate data were fitted to eq. 3 or 4.


Enzyme

Vmax

Km (UDPGA)

KAX (UDPGA)

Km (Substrate)

KsiB

Substrate
pmol min-1 mg-1 μM μM
UGT1A1 2234 ± 209 1217 ± 128 755 ± 71 49.5 ± 6.9 80 ± 10 Ethinylestradiol
574 ± 54 391 ± 55 3716 ± 1139 Umbelliferonea
UGT1A3 1015 ± 112 508 ± 78 1302 ± 271 Entacaponea
68 ± 14 19.3 ± 8.1 469 ± 324 Ethinylestradiola
UGT1A6 22,910 ± 602 644 ± 22 1419 ± 70 4-Nitrophenol*
UGT1A7 664 ± 47 5.99 ± 1.3 320 ± 107 4-Hydroxyestronea
UGT1A8 3641 ± 332 1759 ± 183 796 ± 74.5 119 ± 16 612 ± 131 Entacapone
UGT1A9 10,722 ± 158 299 ± 5.55 145 ± 11.0 26.3 ± 1.1 2406 ± 155 Entacapone
UGT1A10
5469 ± 107
944 ± 28.1
496 ± 34.8
37.4 ± 1.6
2800 ± 262
Entacapone
  • a The kinetic parameters were determined at 1 mM UDPGA using eq. 4.